1. Field of the Invention
The present invention relates generally to resilient pads, and the like for supporting the human body in a seat or on a bed, and more particularly relates to improvements in foamed material pads intended to better distribute pressure on the skin to avoid injury and in particular to prevent formation of decubitus ulcers, also known as bed sores.
A great deal of effort has been expended to devise and improve pads of various types to distribute as evenly as possible the pressure exerted on the body of a person resting thereon. The irregular shape and weight distribution of the human anatomy causes certain portions of the body to carry a disproportionate pressure load when the body is supported on a plane surface, even if that surface is quite resilient. In a bed-ridden person resting supine on a horizontal, uniform surface, areas of high local pressure are typically found at the back of the heels, the sacrum area, and the back of the head. In a side position, areas of peak pressure typically occur in the hip bone or trochanter area in contact with the supporting surface.
Protracted pressure against any portion of the skin has the effect of diminishing or cutting off peripheral vascular flow to that area. If impairment of blood flow to the affected area is sufficiently prolonged, the tissues underlying the affected skin area will be starved of nutrients and suffer progressive damage. Typically it is the underlying soft tissues which are first damaged, until eventually the skin undergoes necrosis and ulcerates in progressive manner, and unless the pressure on the area is removed, such ulcers can become deep open wounds which are difficult to treat and slow to heal.
It is known to make apertures or holes in a foam pad to accommodate and relieve pressure against anatomical protuberances. For example, one or more circular holes can be located on the pad to underlie the coccyx of the patient. Other holes can be placed under the head, the heels, and generally under any bony protrusion susceptible to ulceration or damage during protracted confinement to bedrest or a chair. Such holes in prior foam pads have been characterized by straight interior walls, that is, walls which are perpendicular to the foam pad surface, regardless of the shape of the hole opening on the pad surface. The response of the pad surface to weight loading in the vicinity of such a straight walled hole is influenced somewhat by the hole, since the pad material is deprived of support at the interior wall defined by the hole. A load placed on the top surface in the vicinity of a straight walled hole may find less support than the same load placed at a point further removed from the hole because in the former case the foam material is able to bulge into the hole and thus yields more readily. At the pad surface however, the edge of the hole remains relatively well supported and can press into the skin tissues of a person lying thereon. Because of the relatively sharp transition in pressure against the tissues at the edge, a straight walled opening or cavity in the support surface of the foam pad can cause the skin and underlying tissues to extrude into the hole. This sharp transition creates shear stress in the skin and underlying tissues which tends to accelerate breakdown and eventual ulceration of the tissues. What is needed therefore is a means to reduce or eliminate shear stress in the tissues of a patient at the edge of holes or cavities in a foam pad, so that holes and cavities can be better used to relieve skin pressure and conform the pad surface to anatomical protuberances and irregularities.
Still another benefit of this invention resides in improved control over edema, the accumulation of fluid in tissues which extrude into a hole or depression in the supporting surface. In the improvement of this invention, the cavity edge becomes depressed and rounded when under load, the tissues are largely prevented from extruding into the cavity thus reducing the likelyhood of edema and consequent tissue damage.